Election campaign, the head of Government Stephen Harper says that marijuana is "infinitely worse" than tobacco.

It marks his opposition to the political project of one of his main opponents to legalize its use for recreational purposes as did some time ago the United States Washington, Alaska, Oregon, and Colorado.

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MJ Milloy is an infectious disease epidemiologist who studies the therapeutic effects of marijuana at the Centre for excellence in HIV/AIDS on the Canadian West Coast.

It is one of those who have chastised Mr. Harper for his assertion that there is "overwhelming and growing scientific and medical evidence on the negative effects of marijuana long term. ''

Dr. Milloy indicates that there are risks short-term obvious, as driving during the use of cannabis, but there is no evidence that moderate long-term use results in significant costs to health.

Some research have linked using long term during adolescence to the problems of mental health such as psychosis and schizophrenia. But Dr. Milloy said that no causal link has been proved and that some young people may be genetically predisposed to such problems of mental health.